New member, potentially stupid north-facing roof question

[nok32]

Hi, I was googling trying to figure this out and couldn't find the answer.. maybe it is a dumb idea, at the very least, I know it is "not recommended", but as to the "why".. I dunno:

Is there any problem with mounting PV modules on the north-facing section of a ridge roof and tilting them up to point at the proper south-facing angle? Let's say the roof has a 12:12 pitch (45deg). I am not concerned about aesthetics or aesthetic-based code considerations. Please only point out any valid structural and performance issues. The one consideration I can see is high winds near the ridge peak. That is valid.. is that the main concern? Maybe there is still some practical way to work it.. some kind of wind shroud? I am curious to see any links or photos to successful installs of this sort. Thanks!

[pleppik]

Hi, I was googling trying to figure this out and couldn't find the answer.. maybe it is a dumb idea, at the very least, I know it is "not recommended", but as to the "why".. I dunno:

Is there any problem with mounting PV modules on the north-facing section of a ridge roof and tilting them up to point at the proper south-facing angle? Let's say the roof has a 12:12 pitch (45deg). I am not concerned about aesthetics or aesthetic-based code considerations. Please only point out any valid structural and performance issues. The one consideration I can see is high winds near the ridge peak. That is valid.. is that the main concern? Maybe there is still some practical way to work it.. some kind of wind shroud? I am curious to see any links or photos to successful installs of this sort. Thanks!

I guess my question is, why would you want to do this? I'm seeing a lot of expense and complexity, and little to no benefit.

Wind is likely to be the main concern, since what you're describing is pretty much a giant sail on the roof of your house. Personally, I would want a structural engineer to review any such scheme, to make sure it's not going to rip the entire roof off the house in a windstorm.

Also, depending on where you live, many municipalities have height limits in their zoning codes. If the panels extend above the ridgeline of your house you may need to get a variance (or at least check to make sure it's allowed).

[nok32]

The rafters are 16ft. What if the panels are mounted lower than the ridge? Would this reduce winter exposure too much? They would also have a windbreak created by another adjacent roof structure to the east. Could the underside of the module frame be covered, such that wind could not get underneath the arrays?

The basic reasoning for doing this is that all the south-facing roof is glazed. I am miles away from anyone who would care about code blah blah, so that is not a concern, unless it is related to safety, structural integrity or some other valid reason besides "the neighbors".

[J.P.M.]

The short answer to your question is no, provided the wind loading and other structural calcs are done correctly. Those calculations, while different for every application, are fairly straightforward. A good solar vendor knows this and will not be intimidated by some design work that may need to be farmed out, done and sealed by a P.E.

I did my own calcs/design for a water cooled thermal collector back in the day, had the design reviewed and checked by another P.E. and sealed it myself. That was a pretty non standard design and as I recall probably took 2-3 hrs. Id guess things are a bit more standardized these days for PV.

A bigger cost may well be due to any modifications necessary to the support structure that may need beefing up from the added external load combinations. South facing, tilted arrays on north facing roofs can be a very viable way to use those surfaces.

[nok32]

Excellent, I love it when I am told what I want to hear.

But, really, I am glad to know the possibility exists and google doesn't know it all. Thanks. I wonder though if anyone has some example photos of this type of install.

[pleppik]

The rafters are 16ft. What if the panels are mounted lower than the ridge? Would this reduce winter exposure too much?

You should be able to get a solar installer to do a site survey and calculate exactly how much production you will lose from shading by the roof, nearly trees, etc. An experienced installer may also be able to offer some alternative ideas for placement of the solar panels.

[sensij]

You might try to get in touch with forum user "SoCalSolar". I've seen a few posts from that user mentioning reverse tilt installations, and IRL works for a solar installation company and may have some ideas about how to go about getting it designed.

[SoCalsolar]

Tilt Kit very doable

Tilt Kits very doable not usually difficult with some caveats. They don't do much for the appearance of most roof surfaces. Depending on the angle of the panels flat usually doesn't require any exotic engineering. If you tilt them at a positive angle in relation to the roof more complex engineering calculations are usually required along with additional structural support. What most people don't realize is that a flat array will produce slightly more that an East or West facing array tilted at 22 degrees. However if you have TOU rates than you ought to be thinking more about the value that solar produces and not solely the quantity. Tilt Kit Sketch.png Uploaded a pic hope it helps.

[J.P.M.]

Tilt Kits very doable not usually difficult with some caveats. They don't do much for the appearance of most roof surfaces. Depending on the angle of the panels flat usually doesn't require any exotic engineering. If you tilt them at a positive angle in relation to the roof more complex engineering calculations are usually required along with additional structural support. What most people don't realize is that a flat array will produce slightly more that an East or West facing array tilted at 22 degrees. However if you have TOU rates than you ought to be thinking more about the value that solar produces and not solely the quantity. [ATTACH=CONFIG]5912[/ATTACH] Uploaded a pic hope it helps.

I'd remember that flat arrays usually and probably foul up quicker than sloped arrays, and that tilted, south facing is usually the first place to start in any search for max. production or max. bill offset, which, particularly with T.O.U. may require different orientations for either.

[SoCalsolar]

Flat arrays

Flat arrays will get dirtier more quickly than sloped and TOU is like a diet, it largely depends on how strict you are although having a good Azimuth is like somebody who has a high metabolism it makes it a lot easier to shed pounds and shed dollars from the e-bill.

[J.P.M.]

Flat arrays will get dirtier more quickly than sloped and TOU is like a diet, it largely depends on how strict you are although having a good Azimuth is like somebody who has a high metabolism it makes it a lot easier to shed pounds and shed dollars from the e-bill.

FWIW, mostly +1.

[JFinch57]

Roof Peak Mounted Panels

Newbie here, just joined and saw this thread. I've seen it done at the installer's house that did the 38KW system on my business. The roof is south facing but the panels are over the peak and essentially what you want to do. His name is Dave Sims from Ecological Systems, 1634 Martin Road, Wall Twp. NJ 07753. Clearly visible on Google/Bing maps. It appears that there are 5 rows above the peak!!! A picture is on the bottom of this page on their website http://ecologicalnj.com/energyeff.html . Dave Ecological systems.JPG

[SunEagle]

Newbie here, just joined and saw this thread. I've seen it done at the installer's house that did the 38KW system on my business. The roof is south facing but the panels are over the peak and essentially what you want to do. His name is Dave Sims from Ecological Systems, 1634 Martin Road, Wall Twp. NJ 07753. Clearly visible on Google/Bing maps. It appears that there are 5 rows above the peak!!! A picture is on the bottom of this page on their website http://ecologicalnj.com/energyeff.html . [ATTACH=CONFIG]5914[/ATTACH]

Interesting installation. He does have a lot of panels and those 5 rows of 7 were probably installed due to the amount of shade he gets on the other panels.

I also don't see how that wind turban will work with some many tall trees around it.

[JFinch57]

I doubt that there are many shading issues, he's in the business and has one of those Solmetric SunEye tools. As far as the wind turbine goes it was installed just for show because Dave is in the business. Permits were obtained in a shady fashion using a ham radio permit and the town made him take it down about 4 years ago. I recall it was up for several years while he fought them. At that time I lived around the corner and tried to get legitimate approval for a 20KW turbine on a 120' tower and got shot down because of his battle. If they gave it to me they would have to let him have his, political BS! I even had NJ Clean Energy approval and they were going to give me over $50K toward the project. Spent $3,500 trying to get town planning board and variance approval, oh well!!!

[peakbagger]

If you don't have to worry about building code and don't mind having the panels end up on the ground in high wind conditions then you don't need to do structural calculations. If you wanted for them to be designed to meet expected wind conditions then the structure is going to be very beefy and you may have to modify the existing roof structure to take the point loads from the new mounts.